MRT-compatible valve prosthesis for use in the human or animal body for replacement of an organ valve or a vessel valve

ABSTRACT

The invention relates to a biological or artificial valve prosthesis ( 4, 5 ) for use in the human or animal body for replacement of an organ valve or a vessel valve, in particular a cardiac valve prosthesis or venous valve prosthesis, with a stent ( 8 ) or without a stent, with a supporting valve framework, with at least one valve ( 7 ) and with at least one conductor loop ( 2 ) that forms the inductance of an electrical resonance circuit. In order to provide a simple and inexpensive valve prosthesis that can be viewed in the MR imaging technique and is also easy to implant, the invention proposes that the at least one conductor loop ( 2 ) forms the valve framework and/or the valve ( 7 ) or supporting areas of the valve framework and/or supporting areas of the valve ( 7 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/066,810, filed Mar. 13, 2008, now U.S. Pat. No. 8,167,928, which is anational stage application under 35 U.S.C. 371 of PCT Application No.PCT/EP2006/008964 having an international filing date of Sep. 14, 2006,which designated the United States, which PCT application claimed thebenefit of German Application Serial No. 10 2005 044 009.6, filed Sep.14, 2005, the entire disclosure of each of which are hereby incorporatedherein by reference.

SUMMARY

The invention relates to a biological or artificial valve prosthesis foruse in the human or animal body for the replacement of an organ valve ora vessel valve, in particular a cardiac valve prosthesis or venous valveprosthesis, with a stent or without a stent, with a supporting valveframework, with at least one valve and with at least one conductor loopwhich forms the inductance of an electrical resonance circuit.

Biologically speaking, venous valves are located in the deep leg veins.They serve to prevent the backflow of the venous blood into the limbs.Through compression of the veins during the tensing of the muscles, theblood is transported in the direction of the heart. The valves canbecome leaky (insufficient) or lose their function through theaccumulation of coagulated blood (leg vein thrombosis). Venous valveprostheses are currently under development and generally consist of astent framework made of self-expanding material such as, for example,nitinol or a steel framework into which either a valve made of polymeror a thin film of nitinol or a metal mesh. The valve function canoptionally be restored surgically through the installation of a wovensleeve with narrowing of the veins.

The cardiac valves are located inside of the heart and separate theatria from the ventricles and ensure, as one-way valves, that the bloodflows in the correct direction. The heart has four valves, of which twobelong to the right and two belong to the left heart. The blood flowsout of the venous vessels into the atrium or the auricle, from therethrough a valve into the ventricle and from there, in turn, through avalve into the vessels of the systemic or pulmonary circulation. Thecardiac valves consist of thin, stable layers of connective tissue whichare formed in the manner of pockets (aortic valve and pulmonary valve)or sails (mitral valve and tricuspid valve). Like the rest of theheart's interior, they are covered by the thin interior skin of theheart (endocardium).

In the case of considerable restriction of the valve function as aresult of inborn or acquired defects such as valve insufficiency orvalve stenosis, the replacement of the cardiac valve with a prosthesisis necessary. There are two types of cardiac valve prostheses, namelythe biological and mechanical cardiac valve. The biological cardiacvalves are also called stentless valve prostheses, since they do notcontain a stabilizing framework. The valves are prepared from pig heartvalves or from the tissue of the bovine pericardium or the submucosa ofthe small intestines of pigs or from human endothelial cells on collagenfibers or plastic or metal nets/films cultivated according to the shapeand function of the human cardiac valve. In most cases, these prosthesesdo not necessitate lifelong administration of oral anticoagulant to thinthe blood but rather only a temporary anticoagulant in the first fewmonths after the operation.

Mechanical valves consist of metal and/or plastic. They require lifelonganticoagulation but have an almost unlimited service life. The valvesare encased by a woven sleeve with which they are stitched into theposition of the former defective cardiac valve.

Operations for the replacement of defective cardiac valves are performedin heart surgery under induced (cardioplegic, diastolic) cardiac arrestin order to achieve a blood-free, calm operation situs. In this state, awide variety of types of cardiac valves are stitched in place. Ascompensation for this cardiac arrest, it is first necessary to maintaincirculation using a heart-lung machine, and the main artery (aorta) mustalso be clamped off. These measures are associated with significant sideeffects and complications.

Current developments are consequently aimed in the direction of animplantation of collapsible cardiac valve prostheses which are insertedand placed via catheter. The basis of the prostheses is a stent-likeframework into which either a biological valve or a polymer valve isfitted. The implantation is performed by means of balloon dilation orself-expansion. However, it is disadvantageous that the stent frameworksof the collapsible, known cardiac valve prostheses impair MRTvisualization and hence interfere with a very simple check of the valvefunction.

A percutaneously implantable cardiac valve prosthesis can significantlyreduce the risk that is present during an open operation; however, theprecise positioning of an X-ray control is not possible, since the softtissue of the heart is not represented and only appears through theadministration of contrast medium through the perfused area. Animplantation through MRT imaging would be advantageous, since both theflowing blood and the heart tissue are represented without contrastmedium.

According to current state of the art, the collapsible cardiac valvescurrently available on the market do not yet have optimalcharacteristics, given that the function of the implants can becontrolled only to a limited extent and only invasively through the useof catheters, X-ray radiation and contrast media with considerable risksand burdens for the patients and the medical personnel. Both during theplacement of the implant and during the required follow-up examinations,long periods of fluoroscopy are often necessary. They last between 10and 15 minutes but can reasonably last for 60 minutes or more. Sideeffects such as the development of radiation abscesses (ulceration) canresult from the long exposure periods, which can lead to skin cancer.The long periods of fluoroscopy and correspondingly high dose levelshave also resulted in radiation damage suffered by patients who havebeen subjected to a cardiac intervention. The Federal Department ofRadiation Protection has determined in this regard that the reduction ofthe exposure to radiation in medical diagnosis is of considerablesignificance.

Examination techniques using magnetic resonance tomography (MRT) cancontribute significantly to the reduction of examination proceduresinvolving X-ray diagnosis and nuclear medicine. In addition to the lackof radiation exposure, magnetic resonance tomography has otheradvantages in comparison to X-ray techniques such as computer tomographyand fluoroscopy. It offers an outstanding soft tissue contrast and isthe only layered imaging technique that offers completely free layerpositioning. Spatially resolved spectrometric techniques allow for afunctional analysis of biochemical processes in the human body.Likewise, vessels can be represented directly in the operation areawithout the use of contrast media. In open magnetic resonancetomography, the physician has access to the patient and, as a result,can perform aspiration and operations under direct MRT control.Catheterizations can also be performed well in closed high-field deviceswith modern imaging.

A cardiac valve prosthesis of the type mentioned at the outset isalready known from EP 1 092 985 A2, from which the MR imaging techniqueis also derived, to which express reference is made here. The knowncardiac valve prosthesis has an external valve framework on which theactual cardiac valve is movably supported. Both coils and capacitors areprovided on the annular supporting framework to form the resonantcircuit. Of advantage in the known cardiac valve prosthesis is that itcan be represented outstandingly using the MR imaging technique. Adisadvantage is that this prosthesis cannot be implanted percutaneously.

While conventional collapsible cardiac valves can be implantedpercutaneously, imaging in magnetic resonance tomographs currently hasthe following considerable disadvantages:

-   -   a pronounced tendency toward interference and artifacts due to        the metals used,    -   due to the Faraday cage effect, the insides of a metal implant        are shielded and observable only with difficulty,    -   metal- or plastic-based valve mechanisms either do not provide a        signal or lead to magnetic field inhomogenization,    -   in the moved metal components of the valve mechanism in the        strong magnetic field, undesired inductive effects can occur,    -   the biological valves consist predominantly of collagen fibers        that provide no signal or only a weak one, and few cells, so        that direct MRT imaging is impeded,    -   the temporal and spatial resolutions are insufficient for the        complete diagnosis of the valve and its functions.

As a consequence of the aforementioned problems, conventionalcollapsible cardiac valves, which usually consist of stainless steelalloys or nitinol, are not usable or only insufficiently usable for MRTexaminations of the valve functions and the correct positions of theprosthesis.

It is therefore the object of the present invention to make available avalve prosthesis of the type mentioned at the outset in which theaforedescribed disadvantages are avoided.

The aforementioned object is achieved according to the invention in avalve prosthesis in that the at least one conductor loop forms the valveframework and/or the valve and/or supporting areas of the valveframework and/or supporting areas of the valve of the prosthesis. Thearrangement according to the invention offers a series of significantadvantages, with the at least one conductor loop assuming a plurality offunctions. First, the conductor loop forms the MR resonant circuit andthus ensures the MR function. Moreover, the conductor loop forms thevalve framework or at least supporting areas of the valve framework forthe mounting of the valve. Moreover, the conductor loop can also formthe valve or supporting areas of the valve. Since the conductor loopassumes a supporting function in the prosthesis according to theinvention, it is also possible to keep the throughput opening of theprosthesis open by means of the conductor loop. Finally, an anchoring orfastening function results especially if the conductor loop additionallycomprises anchoring means.

Preferably, a provision is made in the invention that the stent and/orthe valve framework has cells of varying sizes on its exterior, which isto say on the external circumferential casing surface. Resulting is alattice or net arrangement on the exterior, with it then being possibleto provide a plurality of uniformly-sized as well as differently-sizedcells or openings or windows.

Moreover, due to the fact that the conductor loop forms the valveframework, it is quite easily possible to design the prosthesis to becompletely collapsible or expandable and hence percutaneouslyimplantable.

Finally, the invention consequently results in a valve prosthesiscomprising at least one closed resonant circuit with an inductance andpreferably a capacitance which is percutaneously implantable incollapsible arrangement, with an optimal stabilization and anchoring ofthe prosthesis being achieved by means of the resonant circuitconstruction and geometry. Here, the electrical resonance circuitgenerates a signal response which is detected and represented in aspatially resolved manner by means of at least one external receptioncoil, so that the MR imaging of the valve and of its function isimproved. Moreover, the valve prosthesis according to the invention isparticularly well-suited to implanting under MR imaging, since theopening as well as the positioning and anchoring can be determinedprecisely.

To anchor the conductor loop or the resonant circuit, it is expedient toprovide anchoring means, for example in the form of eyelets, hooks orthe like. In this connection, it is favorable to embody the anchoringmeans in one piece with the conductor loop, so that no furthercomponents are necessary for anchoring. However, it is also possible inprinciple to design the eyelets, hooks or the like as separatecomponents which are then immovably fastened to the coil wire. Inconnection with the anchoring means, it is important that they notprotrude in the compressed state of the valve prosthesis over same and,if the valve prosthesis is located at the site of implantation, becomeactive and can be used to fasten the prosthesis to the surroundingtissue only after opening. Through the integration and immediateproximity of the anchoring to the resonant circuit, improvement isachieved particularly of the correct positioning of the prosthesis underMRT as well as the subsequent diagnosis with respect to leakiness of thevalve site.

The present invention is notably suitable in connection with biological,stentless valve prostheses, particularly heterologous ones from ananimal, such as the cardiac valve or the pericardium of a pig or thepericardium of a cow, or homologous and isologous ones from humantissues and cells, with the conductor loop being enclosed in these casesby the biological cardiac valve. Finally, in this case the biologicalcardiac valve contains the conductor loop and hence the resonantcircuit. As will readily be understood in this context, the conductorloop has a shape which is adapted to the natural cardiac valve, with thevalve shoulders or leaves being encompassed in at least one coil and thebase of the cardiac valve being enclosed by a cylinder coil.

Particularly in connection with a biological cardiac valve, it isexpedient that bioresorbable components which stabilize and seal off thevalve prosthesis for implantation be provided. Here, the at least oneconductor loop is then provided for implantation in a biologicalcomponent of the valve prosthesis and remains there after thebioresorbable components have been broken down in the body. Thebioresorbable components therefore merely serve to stabilize the valveprosthesis up to the time immediately following the implantation.However, the ingrown cardiac valve continues to have advantageouscharacteristics for MRT imaging in order to be able to representoptimally in the MRT defects occurring over the long term, such as wearand tissue reaction, and to initiate a treatment or a replacement in atimely manner.

While it is possible in principle to design the prosthesis without astent, it goes without saying that prostheses with a stent are alsopossible. In this case, a provision is then made according to theinvention that the valve framework and the valve are fixed by theconductor loop at least in part in a self-opening or mechanically,particularly hydraulically or fluidly, expandable stent such that,during compression and subsequent opening, both the valve framework andthe valve as well as the conductor loop return to the desired shape,position and geometry, hence simultaneously achieving the necessarysealing-off of the prosthesis in its bed. In this connection, it isparticularly preferred that the entire mechanism not only be held by theconductor loop but that the conductor loop also serve to fasten thevalve on the stent. Here, at least areas of the conductor loop are thendrawn out of the stent. These areas can also be used for anchoring inthe surrounding tissue and hence constitute an anchoring means.

Preferably, a provision can be made that the framework forms severalresonant circuits with different resonant frequencies, each with aconductor loop, or that several resonant circuits are coupled to eachother with only one conductor loop. In this manner, not only is thesupporting function of the valve framework improved, but the cardiacvalve replacement can consequently also be used in different MRTs. It ispreferred in this connection that the valve framework have severaldifferent coil shapes, i.e. different coil geometries such as, forexample, cylinder, saddle and bird cage coils.

In addition, at least one coil of the resonant circuit can also have ameander structure. It is also advantageous if the conductor loop or theconductor web itself is embodied to be meander-shaped. Resulting fromthis embodiment is a targeted and defined collapsibility and expansion,with the surface of the coil being increasable and the elasticity in thebed tissue being improved. At the same time, fatigue failures can becombated with this embodiment.

Since the shape of the conductor loop can be selected at will, it isexpedient that, in a biological cardiac valve, the conductor loop havethe shape of a natural cardiac valve and at least two loops of theconductor loop be provided which form a cylindrical shape with theirsurfaces, enclose the natural valve shape and keep the outlets of thecoronary vessels open in the area between the loops.

In order to obtain a compact prosthesis, it is expedient that theadditional capacitor belonging to the resonant circuit be fastened orarranged on and/or in the valve prosthesis and/or integrated into thedesign of the valve prosthesis.

Here, in connection with the anchoring, the inductance and/orcapacitance of the resonant circuit is provided at least in part forintegration into the tissue enclosing the valve prosthesis for thepurpose of stitching on, anchoring, and/or sealing.

In order to set the external parasitic capacitance, the conductor loopis coated with a nonconductor as a dielectric layer, particularly withplastic and/or ceramic. In this manner, the desired parasiticcapacitance can be set on the one hand by way of the selection andtechnique of the coating and on the other hand by way of the thicknessof the coating, which is at least 1 nanometer. Moreover, through thedielectric layer and the spacing between the loops of the at least oneconductor loop, an internal capacitance is formed whose magnitude can beadjusted through the type of dielectric layer and the spacing of theindividual loops.

Here, the outer coating or dielectric layer preferably consists ofTeflon, polyester, polyurethane, parylene or other suitable polymers.Besides the insulating function and the formation of the parasitic andinternal capacitance, the dielectric layer can have the additional taskof attaching or fixing another coil belonging to the resonant circuitand/or at least one capacitance on or in the framework of theprosthesis.

In addition, it can also be expedient to attach or fix the conductorloop or coil on the valve framework or the valve prosthesis by means ofa layer. Accordingly, the valve prosthesis or the valve framework can becoated with an appropriate material.

Finally, the resonant circuit of the cardiac valve prosthesis accordingto the invention is embodied such that the resonant circuit has aresonant frequency, particularly in the high-frequency range, namely inthe range between 8 to 400 MHz, which corresponds to the frequency of anexternal magnetic field, particularly of an MR tomography.

In principle, a provision can be made that the conductor loop bemanufactured from a wire or a tube or from sheet metal cut from amaterial with a low magnetic susceptibility such as, for example,nitinol or a good electric conductivity such a noble metal or a noblemetal alloy or from a material with a low magnetic susceptibility and agood electric conductivity such as, for example, tantalum.Alternatively, however, it is also possible that the conductor loop havea non-conductive conductor support which is coated with a conductivematerial, particularly gold, platinum, tantalum and/or conductivealloys. In addition, however, it is also possible that the conductorsupport be conductive and coated with an appropriate material in orderto improve its electrical conductivity. It is favorable to implement theconductor loop through the coating of the valve prosthesis with aconductive material. Preferably, the application of the coating occursby means of vapor deposition or sputtering (PVD or CVD).

A low magnetic susceptibility is present in materials which have adielectric constant of much greater than 1. Accordingly, for example,the dielectric constant of the magnetic susceptibility of nitinol liesat 3·10⁶. By contrast, materials with a good electrical conductivity in[S/m] have values which are much greater than 1. Thus, the electricalconductivity of titanium is 2.34·10⁶ S/m, whereas that of copper isbetween 35 to 58·10⁶ S/m.

In connection with the application of the coating, it is expedientparticularly with polymers, ceramic, nickel titanium and titanium as thematerial of the conductor support to apply a base layer onto thismaterial in order to improve the adhesion of the coating. The base layeris then ultimately an adhesion promoter.

In addition to the aforedescribed parasitic and/or internal capacitance,it is expedient, incidentally, that an additional capacitance beimplemented by means of a capacitor. Consequently, it is then notnecessary to implement special shapes or special coatings of theconductor loop in order to achieve prescribed internal and parasiticcapacitances.

In order to facilitate the implantation and in order to be able tomonitor both the opening and the function of the valve prosthesisaccording to the invention, a provision is made in a collapsible andexpandable valve prosthesis that it is designed such that, duringexpansion, the resonant frequency is changed by changing the coilgeometry of the resonant circuit and can be set to the resonantfrequency of the MR tomograph.

The present invention further relates to a percutaneously implantableand expandable biological or artificial valve prosthesis for use in thehuman and/or animal body for the replacement of an organ valve or vesselvalve, with at least one valve mechanism provided with a valve and witha stent with a casing made of biocompatible material, with the stentbeing enclosed at the functional height of the valve by at least oneconductor loop which forms the inductance of an electrical resonancecircuit.

In contrast to the aforedescribed form of embodiment, the valveprosthesis itself or the valve framework or even the valve is not formedby the conductor loop. In this embodiment, the resonant circuit is fixedaround the stent at the functional height of the valve in the form ofthe at least one conductor loop.

In the aforementioned embodiment, there are various fundamentalalternatives with respect to the arrangement of the conductor loop. Onthe one hand, the conductor loop can be arranged around the supportingframework of the stent. However, since the supporting framework of thestent can impair the MR function, it is particularly expedient, on theother hand, that the supporting framework of the stent or supportingareas of the stent framework be formed by the conductor loop. A negativeinfluence of the resonant frequency by a second supporting frameworkcannot occur in this case. Moreover, it is possible that the conductorloop serve to attach the valve mechanism in the stent and be at leastpartially drawn out of the stent for this purpose. Finally, an anchoringof the stent in the valve support can be achieved by means of theconductor loop or commensurate anchoring means of the conductor loop.Here, too, the conductor loop of course has multiple functions as well.

In connection with the aforedescribed embodiment with stent, it goeswithout saying that the valve prosthesis here can have all of theaforementioned features that have been described previously in the valveprosthesis named at the outset independently or in combination.

Finally, the present invention relates to an MRT technique in which analtered signal response is generated in a locally limited area withinand/or outside the valve prosthesis by means of a closed resonantcircuit with an inductance whose resonant frequency is substantiallyequal to the resonant frequency of the directed high-frequency radiationand in which the range with an altered signal response detected by atleast one reception coil is represented in a temporally and spatiallyresolved manner using respiratory triggering and/or ECG triggering.

The aforementioned method facilitates the temporal resolution andcontrolling of the acquisition of the patient to be treated after ECGand respiratory triggering.

BRIEF DESCRIPTION OF THE FIGURES

In the following, sample embodiments of the invention are explained onthe basis of the drawing.

FIGS. 1a-1c show a perspective, schematic view of a biological valveprosthesis,

FIGS. 2a-2b show a perspective, schematic view of other embodiments ofbiological valve prostheses,

FIG. 3 shows a perspective, schematic view of an artificial valveprosthesis with a valve designed as a cap on the base of a solenoidcoil,

FIG. 4 shows a view corresponding to FIG. 3 of a valve prosthesis with avalve designed as a sphere,

FIG. 5 shows a view corresponding to FIG. 3 of a valve prosthesis with avalve designed as a double valve,

FIG. 6 shows a perspective, schematic view of an artificial valveprosthesis with a valve designed as a cap on the basis of a saddle coil,

FIG. 7 shows a view corresponding to FIG. 6 of an artificial valveprosthesis with a valve designed as a sphere,

FIG. 8 shows a view corresponding to FIG. 6 of an artificial valveprosthesis with a valve designed as a double valve,

FIG. 9 shows a perspective, schematic view of an artificial valveprosthesis with a valve designed as a cap on the basis of a solenoidcoil with a meander-shaped conductor loop,

FIG. 10 shows a view corresponding to FIG. 9 of an artificial valveprosthesis with a valve designed as a sphere,

FIG. 11 shows a view corresponding to FIG. 9 of an artificial valveprosthesis with a valve designed as a double valve,

FIGS. 12a-12b show a perspective, schematic view of a biological valveprosthesis in a stent with a saddle coil,

FIG. 13 shows a perspective, schematic view of an artificial valveprosthesis in a stent with a saddle coil,

FIG. 14 shows a perspective, schematic view of an artificial valveprosthesis in a stent with a valve designed as a sphere,

FIG. 15 shows a view corresponding to FIG. 13 of an artificial valveprosthesis with a valve designed as a double valve,

FIG. 16 shows a perspective, schematic view of a biological valveprosthesis with a stent and an external solenoid coil made of anelectrically conductive material formed into a meander,

FIG. 17 shows a perspective, schematic view of a biological cardiacvalve in a stent with an external cylinder coil,

FIGS. 18a-18b show a perspective, schematic view of an artificial valveprosthesis with a stent and an external cylinder coil and a valvedesigned as a cap,

FIGS. 19a-19b show views corresponding to FIG. 18 of an artificial valveprosthesis with a valve designed as a sphere,

FIGS. 20a-20b show views corresponding to FIG. 18 of an artificial valveprosthesis with a valve designed as a double valve,

FIGS. 21a-21b show a perspective, schematic view of an artificial valveprosthesis in a stent with an external solenoid coil made of anelectrically conductive material formed into a meander and a valvedesigned as a cap,

FIGS. 22a-22b show views corresponding to FIG. 21 of an artificial valveprosthesis with a valve designed as a sphere,

FIGS. 23a-23b show views corresponding to FIG. 21 of an artificial valveprosthesis with a valve designed as a double valve,

FIG. 24 shows a schematic view of a valve prosthesis arranged in acatheter,

FIG. 25 shows a schematic view of a valve prosthesis which can beexpanded with a balloon, and

FIGS. 26a-26e show various representations of stents and valveprostheses of cell-equivalent or different size.

DETAILED DESCRIPTION

Depicted in diagram a of FIG. 1 is a biological cardiac valve 1. Thetype and design of the biological cardiac valve 1 is in itself known.Shown in diagram b is a conductor loop 2 which forms the inductance ofan electrical resonance circuit and hence the resonant circuit as such.A comparison of diagrams a and b of FIG. 1 makes it clear that theconductor loop 2, as a closed conductor web, forms three loops 3 whichare arranged together in the shape of a cylinder. The loops 3 of theconductor loop 2 are adapted to the shape of the biological cardiacvalve 1.

Diagram c from FIG. 1 shows the biological valve prosthesis 4, whereinthe conductor loop 2 or the resonant circuit is integrated into thebiological cardiac valve or the biological cardiac valve 1 is insertedinto the conductor loop 2. It is not shown in detail that the conductorloop 2 has at least one capacitance.

The valve prostheses 4 depicted in FIG. 2 differ from the valveprosthesis 4 depicted in FIG. 1 c) in that anchoring means are providedin the form of eyelets and hooks. In the embodiment according to FIG. 2a), hooks and eyelets are located only on the circumferential annulararea of the conductor loop 2, whereas in the embodiment according toFIG. 2 b), anchoring means present in the form of hooks are alsoprovided on the loops.

Also not shown is that the cardiac valve prosthesis can also have onlytwo loops instead of three loops in order to be adapted in this way to adouble atrioventricular valve.

Moreover, it goes without saying that the anchoring means depicted inFIG. 2, for example in the form of hooks and/or eyelets, can beimplemented in all of the conductor loops portrayed in the following,even if this is not presented in detail.

Depicted in FIG. 3 is an artificial valve prosthesis 5 with a conductorloop 2 on the basis of a solenoid coil. The resonant circuit here has acapacitance 6. The artificial valve prosthesis 5 has a valve 7 designedas a cap. In the sample embodiment shown, the conductor loop 2 forms thesupporting valve framework of the valve prosthesis 5. In thisconnection, it should be pointed out that the individual representationsare merely schematic, diagram-like illustrations of the respective valveprostheses 4, 5.

The artificial valve prosthesis 5 depicted in FIG. 4 corresponds to thevalve prosthesis 5 depicted in FIG. 3, but with a sphere provided as avalve 7.

The artificial valve prosthesis 5 depicted in FIG. 5 also corresponds tothe valve prosthesis 5 depicted in FIG. 3, but with a double valveaccording to the double valve principle, which is referred to asdouble-leaf valve in the following, provided as a valve 7.

The valve prosthesis 5 depicted in FIG. 6 corresponds substantially tothe valve prosthesis 5 depicted in FIG. 3, but with a saddle coilprovided instead of a solenoid coil.

The valve prosthesis 5 depicted in FIG. 7 corresponds to that depictedin FIG. 6, but with a sphere provided as a valve 7.

The valve prosthesis 5 depicted in FIG. 8 corresponds to that depictedin FIG. 6, but with a double valve provided as a valve 7.

The artificial valve prosthesis 5 depicted in FIG. 9 is an integratedresonant circuit on the basis of a solenoid coil, as also follows fromFIG. 3. In contrast to the embodiment according to FIG. 3, the conductorloop 2 is designed to have a meander shape. The meander shape of theconductor wire makes it possible in an especially simple manner tocollapse the valve prosthesis 5.

The embodiment according to FIG. 10 corresponds to the embodimentaccording to FIG. 6, but with a sphere provided as a valve 7. In theembodiment shown in FIG. 11, in contrast to the embodiment depicted inFIG. 10, a double valve is provided instead of the sphere.

Shown in FIG. 12 in diagram a is a biological cardiac valve 1. Asfollows from diagram b, the cardiac valve 1 is integrated into a stent8. In addition, a conductor loop 2 embodied as a saddle coil and havinga capacitance 6 is provided as support for the cardiac valve 1 and henceas a framework for the cardiac valve 1. The height of the conductor loop6 corresponds to the height of the cardiac valve 1, so that all relevantareas are able to be covered by way of the conductor loop 2. Moreover,it will readily be understood that, in addition to the saddle coil,another conductor loop 2 can be provided, which is depicted in FIG. 1b .Here, the individual coils can be formed from different conductor loops2 or from a single conductor loop 2.

The embodiments of FIGS. 13 through 15 correspond substantially to theembodiment of FIG. 12, with the embodiments depicted in FIGS. 13 through15 being artificial valve prostheses 5 which are arranged in a stent 8.The respective conductor loop 2 is designed as a saddle coil andarranged inside the stent 8. The conductor loop 2 respectively forms thesupport of the valve prosthesis 5, with a valve being provided in theform of a cap in the embodiment according to FIG. 13, in the form of asphere in the embodiment according to FIG. 14 and in the form of adouble valve in the embodiment according to FIG. 15.

Represented in each of FIGS. 16 to 23 are embodiments in which therespective valve prosthesis 4, 5 has a stent 8 into which a biologicalcardiac valve 1 or an artificial cardiac valve 9 is integrated as avalve mechanism. In each case, the stent 8 has a sleeve made of abiocompatible material. In addition, the stent 8 is enclosed at thefunctional height of the respective valve of at least one conductor loop2 which forms the inductance of an electrical resonance circuit. In allof the embodiments here as well as in all aforedescribed embodiments,the height of the respective coil or the height extension of theconductor loop is such that a relevant coil field results such that therespective valve is also substantially completely enclosed during thefunction. The ratio of the diameter of the prosthesis opening to theheight of the respective coil lies between 4:1 to 0.5:1.

FIGS. 16 to 23 are also merely schematic representations. The followingoptions are possible in all of the depicted embodiments:

-   1. The stent 8 has a separate supporting framework (not shown) which    spreads the stent 8 and holds it open. The conductor loop 2 is    arranged on the outside around the sleeve of the stent 8 and the    supporting framework in the area of the cardiac valve.-   2. The conductor loop 2 forms at least a portion of the supporting    framework or supporting areas of the framework of the stent 8. Here,    the conductor loop 2 then assumes not only function of the resonant    circuit but rather also the framework function of the stent.-   3. The conductor loop 2 is not only wound around the stent 8 in the    relevant area, but also serves to attach the biological cardiac    valve 1 or the artificial cardiac valve 9. Finally, the cardiac    valve 1, 9 is stitched as a valve mechanism to the conductor loop 2    or parts of the conductor loop 2. In this case, the conductor loop 2    assumes the additional function of attaching the cardiac valve 1, 9    inside the sleeve of the stent 8. Here, outwardly facing areas of    the conductor loop 2 can then have hooks, eyelets or other anchoring    means in order to facilitate the attachment of the stent 8 to the    site of implantation.-   4. Moreover, it is possible to combine two or three of the    aforementioned possibilities. Accordingly, the conductor loop 2, in    addition to alternative 3, can also carry out the function of the    stent 8 as supporting framework at least in the relevant area of the    cardiac valve 1, 9.

FIGS. 16 and 17 each show a biological cardiac valve 1 which is placedinto the stent 8. In the embodiment according to FIG. 16, a solenoidcoil with a meander-shaped conductor loop 2 is located in the relevantarea, i.e. in the area of the cardiac valve 1, whereas the coil isembodied as a cylinder coil in the embodiment according to FIG. 17.

Provided in the embodiment depicted in FIG. 18 is an artificial cardiacvalve 9 which has a support 10 which serves to position the valve 7,which is represented in FIG. 18a . In the diagram according to FIG. 18b, the artificial cardiac valve 9 is placed into the stent 8, with theconductor loop 2 forming a cylinder coil with capacitance 6.

The embodiment depicted in FIG. 19 corresponds substantially to theembodiment depicted in FIG. 18, with a sphere provided as a valve 7. Bycontrast, in the embodiment depicted in FIG. 20, a double valve isprovided as a valve 7.

The embodiment depicted in FIG. 21 corresponds to the embodimentdepicted in FIG. 18, but the conductor loop 2 is embodied as a solenoidcoil and the conductor web 2 is embodied as such in a meander shape.

While a cap is provided as a valve 7 in the embodiment according to FIG.21, a sphere is provided as a valve in the embodiment according to FIG.22. By contrast, in the embodiment according to FIG. 23, a double valveis provided as a valve. There are otherwise no differences between theembodiments according to FIGS. 21, 22 and 23.

In FIGS. 24 and 25, the insertion of a valve prosthesis 5 according tothe invention is represented schematically. The valve prosthesis 5depicted in FIG. 24 is a self-expanding prosthesis which expandsautomatically after arrangement in the site of implantation andwithdrawal of the catheter holding the prosthesis in the collapsedstate. By contrast, the prosthesis 5 of the embodiment depicted in FIG.25 is expanded by means of a balloon that is arranged inside theprosthesis. To this end, the prosthesis is placed in the site ofimplantation using a shuttle catheter which is subsequently withdrawn.After withdrawal of the catheter, the prosthesis initially does not openup. The opening-up is brought about through the expansion of theballoon. To this end, an appropriate medium is fed to the balloon. Afterexpansion, the balloon is pulled out of the prosthesis.

FIG. 26 shows embodiments of valve prostheses according to theinvention. Here, embodiments a), b), c) and d) each show a stent 8, withthe external circumferential casing surface of the stent 8 having alattice or net structure and having a plurality of cells of the same andof different sizes. In principle, the cells, which can also be referredto as windows or openings, can have any shape.

In the embodiment according to FIG. 26 a, two types of cells areprovided, namely predominantly small cells and, in the middle area,larger, approximately triangular-shaped cells.

The embodiment according to FIG. 26 b differs from the embodimentaccording to FIG. 26 a in that three types of cells of different sizesare provided. Located respectively above and below the larger middlecells is a strip with very small cells.

In the embodiment according to FIG. 26 c, the middle cells arerelatively large. Only three large cells are provided.

The embodiment according to FIG. 26 d corresponds substantially to theembodiment according to FIG. 26 c, but more than three large middlecells are provided.

FIG. 26 e shows a valve prosthesis (4) which corresponds substantiallyto the valve prosthesis according to FIG. 1 c, but a plurality of smallcells is provided on the outside.

The invention claimed is:
 1. A biological or artificial valve prosthesisfor use in a human or animal body for replacement of an organ valve or avessel valve, particularly a cardiac valve prosthesis or a venous valveprosthesis, with a supporting valve framework, with at least one valveand with at least one conductor loop which forms the inductance of anelectrical resonance circuit, wherein at least one conductor loop formsthe valve framework and/or the valve or supporting areas of the valveframework and/or supporting areas of the valve, wherein the valveframework and the valve are fixed by the conductor loop in aself-deployable or mechanically expandable stent, so that, in the caseof compression and subsequent deployment, both the valve framework andthe valve and also the conductor loop return to the desired form,position and geometry, and the conductor loop simultaneously serves tofasten the valve on the stent, wherein the resonant circuit has aresonant frequency, which corresponds to the frequency of an externalmagnetic field of an MR tomograph.
 2. The valve prosthesis as set forthin claim 1, wherein at least areas of the conductor loop are drawn outof the stent for anchoring in the surrounding tissue.
 3. The valveprosthesis as set forth in claim 1, wherein the resonant circuit has aresonant frequency, particularly in the range of 8 to 400 MHz.
 4. Thevalve prosthesis as set forth in claim 1, wherein the conductor loop iscut form a wire or a tube from sheet metal and produced from a materialwith a low magnetic susceptibility and/or a good electric conductivity.5. The valve prosthesis as set forth in claim 1, wherein the conductorloop has an electrically conductive or electrically nonconductiveconductor support which is coated by a conductive material, particularlygold, platinum, tantalum, silver or copper and/or conductive alloys. 6.The valve prosthesis as set forth in claim 1, wherein the conductor loopis implemented through a coating of the valve prosthesis with anelectrically conductive material and that the electrically conductive ornon-conductive material of the valve prosthesis is vapor-deposited orsputtered with the electrically conductive material.
 7. The valveprosthesis as set forth in claim 1, wherein with polymers, ceramic,nickel titanium and titanium as a material of the conductor support, abase layer is applied onto the conductor loop in order to improve theadhesion of a coating.
 8. The valve prosthesis as set forth in claim 1,wherein the conductor loop is coated with plastic such as teflon,polyester, polyurethane, parylene or similar polymers, and/or ceramicand that, preferably, the coating has a thickness of at least onenanometer.
 9. The valve prosthesis as set forth in claim 1, wherein anadditional capacitance of the resonance circuit is implemented by acapacitor.
 10. The valve prosthesis as set forth in claim 1, wherein thedielectric layer has the additional task of attaching or fixing anothercoil belonging to the resonant circuit and/or at least one capacitanceon or in the framework of the prosthesis.